On Mondays and Thursdays I often fall very behind during tachanun. I see two options — I can start with the congregation after having listened with proper intent during chazarat hashatz, or I can start during chazarat hashatz and finish so I can pay attention during the Torah reading.
To complicate matters, my custom is to stand with feet together (as I would during my own prayer) during chazarat hashatz so as to be yotzei the Rav's understanding of the Rambam, that there is a separate mitzvah of tefillat hatzibbur b'tzibbur. Starting tachanun early would interrupt that.
If I did start early, would I continually interrupt my V'hu rachum with "baruch hu uvaruch shmo" and "amein" for each bracha, or just interrupt for modim or just birchat kohanim?