I guess you are working where a little change can make a big difference. The following arithmetic may be out by a bit but it gives you an idea of what is going on.
Assuming that we are looking at bottles at around 25C (i.e. 77F) which can be a fairly typical room temperature outside of winter, then (in theory) your 8psi represents 1.2 volumes of CO2. This could result from bottling at slightly more than SG 0.002 above where it finally finished as fully fermented (say, bottled at 1.0022 and finished at 1.000).
So working on the rough "rule of thumb" that a change in SG of 0.002 will result in 1 volume of CO2, you need to bottle at something like SG 1.001 to get around 0.5 volumes of CO2 (if it finishes at 1.000, but of course there is no guarantee that this will be where it finishes).
Measuring SG with some precision at these levels can be a bit problematic and of course temperature can have a big effect on pressure. I have found that bottling a still cider when (I assumed) it was fully fermented is fine at 10C but can be a little spritzig at 20C.
