Letrozole on CD 2-6 vs 5-9

Yaz • 28y | Baby boy born 12 June ‘19! 🧔🏻👩🏻🐱👼🏻👶🏻
I took Letrozole on my last cycle on CD 5-9, and even though I couldn't go in for any ultrasounds that cycle I had sore boobs, cramping, EWCM and all the other symptoms  of ovulation during CD 19-23. The next cycle I took Letrozole during CD 2-6 but no mature follicles at all (CD 12 & 14 scans) :( 
Now what do I do for the next cycle? I've got my dosage upped to 10mg x 5 for the next cycle. My obgyn doesn't even consider recommending CD 5-9, but I'm sure it works better for me... Which days worked for you?