HELP! IUI/Ovulation & Timing of Insem

Hello everyone,
Am hoping someone out there can help.
Just had my 2nd insem with Donor Sperm at Fertility Associates.
My blood test today showed LH at 31 (yesterday was 16). I had an insem yesterday at 16 & today because my LH went up to 31.
My question is, why do F/A do insems on the day of the LH surge when 99.9% of the info I can find online suggests the IUI should be done AFTER the surge. Because the surge indicates ovulation is going to be happening, not is happening.
Frozen sperm lives for 12-24 hours right? So let's take 12 hours to be safe.
Therefore if they do the insem on the day of the surge, it's too early right?
I am reading that ovulation typically takes place 24-36 hours after the surge.
I don't really get a straight answer from F/A but have requested for our 3rd go of IUI that it is done 24 hours after my highest LH surge. Still waiting for approval.
Anyone done this? Advice??? Thanks so much.