Hi Merin, Orin,
I'm not sure what your aim is, but there are many options to filter destinations under the FTL menu. When you engage at a destination to far away it will provide a "nearest destinations" option which will take you as close to your intended destination as possible, based on your current charge.
If you wish to just travel an arbitrary amount you can do this via smart macros. For example if you type FTL followed by a space and then a whole number in the free text box you will travel that many light years. For example typing "FTL 1" will move you one light year to the right, typing "FTL -1" will move you one light year to the left. You can use any amount you wish, so to travel your full charge of 20 you could type "FTL -20".
You can also use waypoints in a similar manner, typing "waypoint 1" will engage straight to waypoint 1 in your computer without any preamble.
In terms of the transfer missions, these are meant to be done by large ships that have long ranges, the missions will filter based on your hold size with a very large range of acceptance - but it should state the distance involved in the mission summary.
I hope this helps.