Happy New Year guys, hope you'll have a great year ahead.
The TA on the bit10 is a bit strange as you 'set distance' in inches / cm and then fine tune in ms. The beauty about phase is that its relative and not absolute. So exact measurements are not really important. You can either enter measured distance to the sub or even leave it at 0.
Play some bass heavy tracks and cut all drivers except the sub and the far mid. Start with the far mid at 0 and add delay to it till you hear and feel the sub from the far mid. You want it at a point where you hear the sub from the far mid without losing the clarity in the midbass/mid range. Our ears cannot locate (front/back or left/right) sound below about 70hz. By getting your sub and far mid in phase your brain and ears are cueing the 70hz and below at the same point as 70hz and over i.e. the far mid. Once you have this dialed in cut your sub and play only the mids and now add delay to the near mid till you get the stage focused upfront. Then play only the far mid and tweet and dial in the tweet and then the near mid and tweet. While doing the mids and tweets you're trying to lift the sound higher than the level of the midbass. Now play all drivers together and you will need to do some minor tweaking.
Mac is spot on, you will wind up with your near mid on a delay between 3.5-3.7ms relative to your sub. The delay between the two mids (assuming door mounted) will be ~ 1-1.2ms. If the tweets are mounted higher than the mids i.e. dash level or pillars, the delay between the tweets would be slightly more than that between the mids. Conversely, the tweets are lower than the mids the delay between the tweets would be slightly less than that between the mids. This is because the PLD between drivers reduces the lower they are mounted.
Frequencies that are phase sensitive, tend to be those played by the mids. Hence getting the mids and the sub/mids in phase is vital. However it is equally important to keep the mids and tweets in phase as well. Doing this is actually tougher than just dialing in the sub and mids.
There are two types of phase. Mechanical phase and acoustic phase. Mechanical phase is when the drivers are firing in an exact sequence based purely on distance of each driver from your ears. Mechanical phase is aimed at exact arrival time. Here measured distances are critical. If you were listening to music in a far field environment, free from early reflections with speakers at different distances, then yes you would want to get them in mechanical phase. But a car is a near field environment with tons of early and late reflections. These reflections are causing phase shifts along with summations and cancellations at different frequencies. Hence mechanical phase is of limited use here. The sequence that Mac is describing ie sub followed by mids together and then tweets together etc is acoustic phase.