A story involving R. Shmuel Salant, R. Seligmann Baer Bamberger, and R. Yosef Carlebach is relevant to the history of the placement, the reason for the placement its connections to Reform, and the ultimate permissibly.
To paraphrase R. Yosef Carlebach quoting Rav Shmuel Salant as cited by R. Dr. Shnayer Leiman's article in Traditon:
Rav Salant gave the following account of his meeting with Rabbi Seligmann Baer Bamberger. "When I entered the synagogue, I... noticed that, contrary to halakhic requirements, the bimma stood directly in front of the Holy Ark instead of in middle of the synagogue. I was astonished, but said to myself that if a zaddiq such as Rabbi Seligmann Baer prays here, surely it is inappropriate for me to raise any questions...As we left the synagogue, the Wuerzburger Rav said to me, 'I am certain that there must be questions you wish to raise about my synagogue practices.' Heaven forbid,' I replied, 'when you approve of a particular practice, it is inappropriate for me to raise any questions.' "Nevertheless,' countered Rabbi Seligmann Baer, 'I know that you were surprised to see... the bimma was not positioned properly.
Let me assure you that I did not do so of my own free will. The dissension caused by the innovators in our community threatened either to render it asunder or to lead it entirely into the Reform camp. I concluded that without concessions I would not be able to save Torah Judaism in Wuerzburg. At the very least, I would have to make concessions in non-essential issues. I consulted with the elderly Gaon, Rabbi Abraham Bing, who gave his consent. Then i spent three consecutive days in fasting and prayer, struggling with my conscience. When I was firmly convinced that concessions were absolutely necessary in order to save my community from far more serious infractions of Jewish law, I too approved. Indeed, due to these relatively small sacrifices, I was able to stem the Reform tide: Rav Salant then said to Rav Bamberger: "There is no need for you to justify your behavior. I knew from the start that it is inappropriate to raise questions about anything you do!" Rabbi Salant went on to say that upon his return to Jerusalem, his rabbinic colleagues in Jerusalem were about to issue a ban against all synagogues that did not have the bimma positioned in the center of the prayer hall. As soon as heard about it, he strenuously voiced his opposition to such a ban, stating before a conference of rabbis as follows: "I have seen one of the greatest zaddiqim of our generation, Rabbi Seligmann Baer Bamberger, pray in such a synagogue. I myself prayed in his synagogue, and even allowed myself to be called up for an aliyah to the Torah there. Clearly, it would be impudent for anyone to ban what he permitted."
However, R. Carlebach did not want people to get the wrong impression so he published the following:
I deeply regret that the anecdote which I published in your journal about the late Wuerzburger Rav, Rabbi Seligmann Baer Bamberger, has given rise to some misunderstanding. Several readers have erroneously concluded from my account that Bamberger regarded the change in position of the bimma an unimportant detail. It is my intention here in a few brief paragraphs to shed light on the topic and set matters straight. The Rambam (11:3) as well as the Shulhan Arukh (Orach Chaim 150:5) make it quite clear that the bimah must be situated in the center of the synagogue. This is of great symbolic significance; it reminds us that the words of the Torah must sound forth from the "midst of the people." From its heavenly origin (symbolized by the elevated Holy Ark and the curtain which veils it), the Torah descends into the "midst" of the Jewish people in order to be proclaimed to the nation as its most precious treasure, as the soul of our souls. It is only Christianity that constantly emphasizes the other-worldly nature of the Word of God. We Jews say regarding our Torah, "It is not in Heaven," Reform Judaism denied its own origin when it imitated the Church and removed the almemar from its central position in the synagogue. Rabbi Seligmann Baer Bamberger would have been the last person to ignore the unique nature of our synagogue...What led him to make his decision was the fact that he was faced with a most difficult dilemma.
Rambam writes as follows in Hilchot Tefillah (11:3):
ומעמידין בימה באמצע הבית כדי שיעלה עליה הקורא בתורה או מי אשר אומר לעם דברי כבושין כדי שישמעו כולם
We put the bimma in the middle of the synagogue so that people can ascend it to read the Torah or to give an inspirational speech that everyone can hear.
The Rama writes similarly in the Shulchan Aruch (Orach Chaim 150:5) :
הגה: ועושין בימה באמצע ב"ה, שיעמוד עליה הקורא בתורה וישמעו כולם. וכשמתפלל הש"צ, פניו כלפי הקדש.