LTE Connection - WIFI Faster thank wired connection (4GE USB PPP Connection)

Hello,

i’ve strange issue regarding my LTE Connection.

  1. speedtest with any device in the wlan network
    download: 43Mbps
    upload: 33Mbps

  2. speedtest with any computer in the wired network
    download: 44Mbps
    upload: 3Mbps

  3. take AP on the same Port as used in example 2 you’ll get the same results as explained in example 1

Setup:
Mikrotik CCR1009-8G-1S
HUAWEI 4G USB Modem
PPP Client MTU 1500 (default settings)
Carrier drei.at

I’ve tried this with RB951G and now with CCR1009-8G-1S same results. The only difference is that the CPU on the RB951G is slow so i’ve changed the device (CPU Spikes because USB Modem needs much CPU)… with the CCR i can see max 40% on 1 Core…

I think there is some issue with diference between window sizes on wired and wlan connections?
Are there any possibility to speed this up via mangle rules?
Any other ideea?