The line is only a stand-in for the circle. It touches the circle at one point and drifts away from it the further along you go. The drift is tiny for ordinary sights, but grows fast when the body is very high, because then the circle is small.

Gap between the straight line and the true circle (miles), at a distance along the line from where they touch
Ho	10 nm	30 nm	60 nm
30°	0.0	0.1	0.3
60°	0.0	0.2	0.9
75°	0.1	0.5	2.0
85°	0.2	1.5	5.9

Keep plotting close to the DR: within 30 miles or so, the line stays within a few tenths of a mile of the circle for altitudes up to about 60°.
Above about 75° the circle is small (a radius of 900 miles at 75°, only 300 at 85°), so the line drifts off it quickly. Avoid very high sights, or plot the circle itself.
The LOP tells you only that you are somewhere on the line. To know where, you need a second line: the fix.

How far to trust it