You are definitely right. If you serve to 55 you get your pension straight away. If you leave before 55 (and have reached the EDP 18/40 point) you get an EDP.
The EDP lump sum is recovered to the extent that it is 'unexpired' and you don't get it back if you are on an FTRS commitment/engagement. This was spelt out above.
The EDP income stream stops and restarts when you leave FTRS.
EDP and FTRS don't mix very well!
If you leave at 55 and join FTRS, there will be abatement of pension but your AFPS 05 (or 75) lump sum is safe.