First reflection points and toe-in

This is one of those it's a personal preference things. The extent to which you decide to use absorption at the points of first reflection should also depend on how close your speaker is to the sidewalls (which are the walls I assume you are talking about since there are many points of first reflection). If your speakers are within say 4 foot of the sidewall and it is a full range speaker and the sidewall is standard home sheetrock construction, you will likely have an SBIR from the sidewall. Whether you want to treat the SBIR or just leave it be is up to you and varies from room to room. You could also have some ringing, which is much easier to treat.

If your question doesn't have anything to do with low frequencies, then I would say you may want to hear your system with no treatment at the sidewall point of first reflection. There's some evidence from Toole that listeners prefer nothing there. Of course, there are much more sophisticated approaches than throwing up some fiberglass panels.

When it comes to really low frequencies and SBIR and ringing, the amount of toe-in isn't going to change the equation very much. In my room, I use modified RPG BAD Arc panels in this position. The reason is primarily related to mitigating an SBIR.

You need a microphone to figure this out.

If you are asking where you should place the BAD panel for maximum bass absorption on sidewall. This would be pretty easy to measure. Ive also done this with BAD panels. Ive got a total of 4 2'x4' BAD panels on each sidewall for SBIR. 2 of them are 4" offset from the wall and 2 are modified with extra 3" fiberglass panel added to back, which includes the BAD arc. I figured out the best location by sending sweeps to each channel and moving the panels to see where they work best. Bass is fairly nondirectional so its best to just measure and move until you find the best spot; its tedious.

Depends somewhat on the speaker's horizontal dispersion (how the sound spreads from the speaker). At LF speakers are omni (at least the ones that fit in most rooms) and become more directional as frequency goes up.