Very low share output from RX580 compared to AMD Vega FE

Hi out there

I have puzzle that I don’t get

I’m running a 7 GPU rig with RX 580 and a 3 GPU rig with AMD Vega FE on Hive OS and the Hiveon pool. I’m using RedTeamMiner for both. Both rigs are updated with the latest OS and Bios

My RX580 runs apprx 28 MH/s and my AMD Vega FE runs apprx. 39 MH/s.
In total I run apprx. 200 MH/s on my RX 580 rig and 110 MH/s on my AMD Vega FE rig.

My RX 580 rig uses apprx. 1.000 watt and my AMD Vega FE rig uses 330 watt

Here comes the puzzle.
On a daily basis, I get 900 shares out of each RX 58 GPU based on a 28 MH/s rate.
That is 32 shares per MH/s.

On a daily basis, I get 2.550 shares out of each Vega FE GPU based on a 39 MH/s rate. That is 64 shares per MH/s . That is twice as many shares per MH/s and even with a lower power consumption.

I simply don’t get that. I thought that MH/s was the only factor that determined the number of shares you would get.

Hope anyone enlights me.