Are the concrete strip and the existing tiles at the same height level as each other at the moment? And also what is the width of that concrete strip?
What is underneath the tiles? Concrete?
If you don't know, do you know how long the tiles have been down for? Looking at the picture, they are in good condition with no cracks. Is there any cracking in the grout or any of the tiles?
Also, if you were to tile over the existing tiles, do you have enough room at the door threshold to allow for the increase in floor height?
If they are suitable to be tiled over, you will need either a soft joint where the tiles meet the concrete (so rather than grouting that joint, you'd Silicon it instead with a colour matching Silicon or install a pre made expansion strip, but that would look ridiculous in there). Or use a decoupling membrane as the concrete and tiles will likely expand and contract at different rates and movement at that joint, could cause stress in the tiles and crack the tiles you put down.
I believe the decoupling membrane would prevent that from being an issue and in a small porch, wont cost you a lot of money at all.
Personally if the tiles are sound and solid and height allows, i'd prime the whole floor with tilemaster prime+ grip, then lay your crack mat on top of this and then tiles on top of that. Tile the whole area, grout the whole area, except for the edges of the floor which you should still Silicon (to allow for expansion).
Of course if anybody disagrees with this approach, please do advise. I've only been going a couple of years and don't profess to know it all whatsoever.
Good luck with your project