Are offspring determined by the horse's stats at the time of breeding or when the horse was at it's "peak"?

If I put a horse into the breeding barn at age 5 with Potential, Speed, etc. of 90, and breed them at age 10, when those stats have dropped, are the offspring's ratings based on those 90-rated stats, or whatever their stats have deteriorated to at the time of breeding?

I usually breed horses until they are 10 years old and find that the offspring will usually breed to the maximum of the sire\dams potential, so if both sire and dam had 90% extra speed rating then their offspring will have 90% extra speed rating about 95% of the time.

If one parent has 70% and the other parent has 90% then about 25% of the time I find the offspring to be at 90%

Each stats seems to be different in my experience, potential as an example seems to be based on the max of the parents with some degree of freedom as to realised or absolute. Constitution seems to be as the horse is when breed hence older horses whose constitution has dropped will typically pass a low rating on, cruising burst is another that seems to be as the horse was not what they are trained too. The foal seems to range between the top and bottom point per parent, so a 90 potential and a 20 potential breed will give a foal between 20 and 90 for the most part.