Thanks for the reply.
Currently it's primo 2.4 Build 9.6.13.267029 (November 2012), but I've also tried earlier and later builds with the same issue. I don't know my screen resolution, only that it's a typical 1 din fold out 7" screen (is there a way for me to tell from within primo?)
here is my current sys.txt
[debug]
skip_eula=1
experimental_features=1

[interface]
show_exit=1
extra_settings=1

[other]
demo_enabled=0

[route]
hnr_ignored_missing_country_ids=*

[vr]
disabled=0

[dynamiccompressor]
compressor=1
a0=56806
thrs=24703
ratio=8
gain=10


[gps]
port=2
baud=9800

[sound]
working=1
dev_channels=2
dev_bits=16
dev_smp_rate=48000
dev_buffer_size=9216
csv_voice_enabled=1
ding=1
effect_volume=255
guidance_volume=255
os_muted=0 ; 1 - sound off
os_volume=255
maneuver_chimes=0
media_volume=255
mic_volume=255
mute_os_key=0
queue_length=200
use_os_volume=1
user_volume=255
voice_volume=255