Hello Arrow,
Line-up allowance simply put is the "distance of runway lost to make the initial line-up and alignment to takeoff direction(by making turn etc)"
It is formalized in JARs but not in FAA. None the less, is recommended to be used by everyone.
Generally 180 or 90 or 0 deg line-ups are used.
180 where you need to back-track.
90 for intersections
0 where you have taxiways entering the runway from its undershoot area (don't know if they have a specific name for that)
I see there are 2 line-up allowances:-
Practical:- Which considers whatever runway lost by average crew to line-up (assuming they follow the taxiway markings)
You should look at line ops to identify this value.
Theoretical minimum:- This is the minimum your aircraft would to make that 180 or 90 deg turn.
This is directly related to the turning radius of the aircraft. Generally found in what is called as airport handling document.
JAA also requires publishing those values as min line-up.
Also 1 point, that line-up is different for reject case as compared to the go case.
Hope that helps.
VK