The most common cause’s of fixed spool reels snapping off during a big cast aside from a bail arm snap over is a combination of a slightly overspooled reel with the shock leader dragging a few loops of extra line off the face of the spool and then getting jammed up in the first guide esp if the lines not been wound on under tension .
Combine that with the initial line lay of the shockleader which for true powercasting should have the knot at the base of the spool so the leader is not getting dragged over that knot at the start. Get both of those wrong and snap off city . Assuming that you are using a good quality line not some springy rope..
My source for that info is from Jock Beloski ex NZ casting champ with fixed spools.
I have only ever played with fixed spools on the casting court and topped out with a 180 odd mtr cast before my fingers were to sore to continue even with them taped up
The issue of moving the base guides is a complex one as it has a lot to do with the reel being used .
Some have a much bigger face to the spool.
Not all reels have the same angle from the reel foot to the spool nor the same distance as well.
Theres a lot of info about it on various rod building forums and theres an lot of discussion about on some of those forums about just how much the blanks flex has to do with it as well.
Its a interesting thing to think about as I have an older kilwell rod that needs to be rebuilt but its a bit of a noodle so the guide spacings are going to be bit of a cast it and see how it works job I think.Its going to be for the wife to use as a light surf rod .