For easier example:
10 exp in 1.5 till level 77
20 exp in 2.0 till level 77
You had 5 exp on 1.5 = 50%. How much times you can put 5 exp in 20? Correct 4. 5+5+5+5 = 20, so in 2.0 you will have 1/4 of 100% ( because you can put 5 exp 4 times in 20 exp ) = 25%. So 50%-25% = 25% lost.
Your friend had 2 exp on 1.5 = 20%. How much times you can put 2 exp in 20? Correct 10. 2+2+2+2+2+2+2+2+2+2, so in 2.0 you will have 1/10 of 100% ( because you can put 2 exp 10 times in 20 exp ) = 100%/10=10%. So 20%-10% = 10% lost your friend.
How much time you can put:
5 exp in 10 exp = 2 times, 2 times in 100% = 50%
5 exp in 20 exp = 4 times, 4 times in 100% = 25%
2 exp in 10 exp = 5 times, 5 times in 100% = 20%
2 exp in 20 exp = 10 times, 10 times in 100% = 10%
Also in this case 10% in 1.5 = 1 exp. 10% in 2.0 = 2 exp. That's why I'm telling that your EXP amount didn't changed.