Wake on LAN from "outside" just works occasionally

hi! thanks in advance for reading. i have a little problem which causes me headaches as it is the ONLY thing which seperates me from my perfect HTPC @ home with my newly bought mac mini:

setup is:

- mac mini late 2009, 4GB ram, 32GB SSD

- mavericks 10.9.2

- netgear router with port 9 and 22 forwarded to the IP of the mac

mac mini config:

ethernet connection, fixed IP

mavericks tweaks:

darkwake = 0 to fully wake it up upon WOL

sleep timers completly disabled

no password required to login

runs plex media server

SSH and screen sharing enabled

alright. that should be it. now lets get to the problem:

WOL within (!!) my OWN WIFI works falwlessy and great. it works each time and is reliable.

additonally to that, I would like to be able to WOL my mac mini from outside. let's say over 3G network or at a friendds WIFI. for this, i bought the app iNet WOL for my iPhone 5. i have configured it to WOL it with my public IP adress thorugh port 9. again, within my own WIFI WOL works all the time.

the problem is: over 3G/outsideWIFI(friend) WOL only works from time to time. it works for 5 minute, i can wake it up, back to sleep, wake it up again. an hour later I am no longer able to do so. later, it probably works again.

it is very unrelaible and inconsistent. what can i do 😟 ?

i have read in a thread, that WOL is poorly implemented by apple. the own Wake on Demand bonjour system from apple works much better, but unfortunatly that requires an airport router which I am not willing to buy.

I can not stress enough: WOL within my own WIFI works all the time. if i am on 3G network, it may work and most of the time it just won't.

I am grateful of any help imaginable! thank you!