I was told that the body only absorbs a % of wut u'r taking (drugs/supplements), even when split into sessions. so, is it a solid #(dosage) or a % ?

Bioavailability.: The dose that is prescribed already takes into account the "bioavailability" of the medication ( which varies depending upon the route of administration) and a host of other processes which may reduce the amount of medication that the body eventually receives. Additionaly people do not have the same body volume and do not always metabolize the drug in the same way. Dosing is an art.