Try the crossed eyes 'find the difference' technique. Which is crossing your eyes such that a third image (a blending of the two images: one from each eye) appears between those two images.
You can easily understand where the difference is because the data is different between the eyes. The difference appears 'ghostly'. In a similar way, data from the mind's eye is different from data from the physical eyes when those two 'streams of data' are blended.
Yes I can do this. I can see the image in the middle the same way as I see each individual image. (But not both at the same time, the outside images get blurry when I focus on the one in the middle).
Anyways, this is nothing like what I experience when I imagine something.
That's what it's like to 'overlay' imagination onto your vision.
But that requires - like the eyes focusing correctly - for the 'imagination vision' and the physical vision to 'line up'
your imagination is more like it's in the the back of the head, yeah?
What helped me 'move' where my imagination was (to the front and center), was to do the flame meditation. Which is to focus on a flame in a dark room for a few seconds, close your eyes, and try to retain the phosphene afterglow in the flame shape. and repeating that until you are able to retain image of the flame while your eyes are closed.
Similarly: 'drawing from memory' - particularly from recent short term memory - was another method that had a profound impact on my ability to visualize.
Both of these take time and commitment, but they have worked for me. They may work for you.
