Using a Vigor 2862Lac

I moved to a new location and I'm currently dependent on my 4G SIM card for internet.
The signal here seems to be weaker than in my previous location.

My RSRP Signal is: -111dBm (Fair)
My RSSI Signal is: -83 dBm (Good)

Max Channel TX Rate: 50 Mbps
Max Channel RX Rate: 150 Mbps

The two LTE antenna are as high as possible on the best window in the place for signal.
The router itself is on the window board below, restricted in positioning by the length of the antenna cables.

Is it possible for me to use LTE antenna extension cables so that I can move the router to a better position for provision of internal wifi while leaving the antenna themselves in the best position found yet.

If so, is there an optimum length of extension cable beyond which the effect on the signal would be degraded?

DrayTek don't have any currently but there are antenna/cables for sale for external use - omni or unidirectional. You want to keep the cable as short as possible as each length introduces more signal loss.

Thanks, I've ordered a pair of 1M and a pair of 2M and will test the effects.

The standard DrayTek antenna (supplied with the router) are not suitable for outdoor use.

My antenna are indoors, stuck to the window receiving the best signal. I want to leave them there and move the router to a more favourable position for providing WiFi internally. Unless the extension cables degrade the signal too much this could work out.
I'm in a location where I can't put equipment on the outside of the building, or I'd gladly go for external antenna.
Is there much chance of finding internal antenna that would pick up better signals than the antenna provided with this router?

I was able to improve my signal using one of these:

https://www.amazon.co.uk/gp/product/B00C1DGFPS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1