My first thought is that most Elan basses are Maple bodies, which have a rather bright sound as the dominant tone. Yours is transparent red, so the top is probably Maple too. Paired with a Maple neck, and you've got one bright bass, even before you turn it on.
The controls inside (2 trimpots) will not change the tone of the bass, just the gain of each pickup. These are usually set so that the ends of rotation of the pan control will have the same volume as each other. I think you really want to focus on your pan control.
Provided that you have the trimpots set so that the pickups are of equal volume, turn the pan pot 100% to the bass pickup (that's the neck pickup). If you then turn the Q switch off (that's up to the ceiling when playing) and rotate the filter control all the way back to the minimum setting (counterclockwise), you'll hear essentially the bassiest tone that bass will produce. Move your right hand so that you are playing above the bass pickup, or even over the truss rod cover. This is a good starting point.
You will probably like the sound with the filter opened up a bit, and you might even want to include some treble pickup and the Q switch depending on the music you are playing. However, since this is a bright beast, you will probably have to use your amplifier if you want it to be beefier.
A v-shaped slot was pretty common for a lot of years here, so unless you think it was modified, or if it's not totally isolating the string movement above it, I wouldn't worry about it.
Also, strings string strings! You might even go crazy and put some flats like D'Addario Chromes on it (you will need extra long scale). At least don't play with steel strings if you are wanting a deeper tone.
Jimmy Johnson plays a Series II with a Mahogany body and Walnut top and back. It's not quite the opposite wood recipe for tone as your Elan, but it's close.
There is a chance that as much as you love the bass, you may want it to be something it isn't. It will always have a bright edge to the tone because of the materials it is made from.
As far as pickup placement goes, unless the string is outside of the magnetic field of the pickup(s), it's not due to the pickups. However, the closer you cram that bass pickup toward the end of the fingerboard, the fuller the tone will be. When you use the pan control (provided you have the trimpots set for equal pickup volume as described above), do you hear the same issue with both pickups? When you say thin, is it a volume issue or a tone issue?
You could change one or both of the pickups to a FatBoy, which has a really wide aperture. If you have a lutherie teacher, I suppose you know a thing or two about using a router. If your Elan has a PJ pickup set, you'll need to make a decorative ring to go around the bass pickup, since the split pickup is wider in one dimension than the FatBoy.
Your profile shows a Spoiler 4-string. Depending on the year, it's a Mahogany or Koa body, which sounds worlds different from the Elan - also most Spoilers are 32 scale, which most people don't like for a 5-string, but some really do. You can temporarily string your Spoiler BEAD to see if you would.
Wow! I'm pretty long-winded tonight. There's lots to discuss, and you have some experimenting to do. Maybe you can also share what type of rig you are using. Between everyone here at the club, we should be able to figure out if the bass can do what you want it to.
