Healing Grace duration reversal

After casting an attack spell it appears the duration of healing grace as well as seconds per tick increases which results in a fractional increase in healing after an attack. e.g.
after attack 9-22 healing every 2seconds for 25 seconds = .72-1.76 points healed/second
.08 points healed/second
no attack 9-22 healing every 1.5 seconds for 19.5 seconds = .69-1.69 points healed/second
.076 points healed/second
Of course I may be missing something or there may be another variable I am not factoring but it just seemed odd at first glance.