Question about using the bucket method to determine if I have a pool leak

I started with a loss of 1 1/2" inches a day in my large in-ground gunite spa. Since there were numerous cracks in the walls I decided to have it fiberglassed. The drain rings were replaced and all fittings were carefully sealed so I am quite confident that nothing outside of the plumbing fittings is leaking. At that point the leaking was reduced to about 1/2” per day according to the bucket test. I concluded that plumbing was leaking somewhere so I purchased a batch of winter plugs and plugged off everything. Now I am showing a loss of ¼” per day. The question I have is how accurate the bucket test is? Is it possible that the large surface area of the pool could cause it to lose more to the air than what is in the bucket? If so is ¼” within that variable? BTW, the water is colder than the air at least until nighttime.

A deep bucket may lose slightly less water than a shallow bucket if the wind is blowing so if you put the bucket on one of the lower steps so the water level is closer to the top of the bucket, you can eliminate any differences between the bucket and the pool.

Unless the bucket is smaller at the top than the bottom (and most are the other way--wider at the top), it's likely to lose water faster than the pool. 5 gallon paint buckets are straight-sided so their rate of loss is the same, given what Mark pointed out.
1/4" per day is a lot (assuming that's 1/4" more than the bucket), and if it's still doing it with plugs, you have a leak in either the pool wall or around the fittings. I can think of a number of causes of leaks when the returns and drains are uncapped. I wondering about a badly cracked return/drain fitting, that seals partially with a plug...But that's idle speculation.