Question about TIME BACK rage power

[Elwin]

I have recently defeated Karador and my Reaper is lvl16. I have read here how powerfull time back ability is and I would love to use it ( would make some harder fights easier, for sure with Karador )..but got 1 problem ... I had only 1 upgrade for time back since all these 15 levels ..so i can use it with units lvl 1-2 only and i do not use lower than lvl 3 ... so useless for me
And now i wonder is there anything determinining upgrades for rage spirits when u level up? Could it be that i dont get any timeback level upgrade ( got rest reduction and rage cost reduction tough) because i dont use it ? Or just i have very hard luck ? According to post on this forum its rather not normal to not have time back at higher level at this stage of game -.-