Other positions and other shapes will (probably) work.  It is possible that another shape in a slightly different position will give the same performance, but this is what the engineer came up with first.  Parameters like slot width and length and x and y position are usually used in optimisation programs in electromagnetic simulation packages (even more so if the design is by hand and uses look-up tables), so for that reason you often end up with rectangular slots and copper, unless, for instance, a genetic algorithm is used to search for a solution, in which case you may end up with a shape similar to the one shown but without right angles and with bent bits that actually do very little.  It is easier and quicker to find an answer by optimisation if the range of shapes you are going to search is limited in some way, provided that it is possible at all within the range you allow.  This design may also have been developed in stages and by experience, using simple easily understood circuit elements to improve the previous performance.