Return value of if/else recursive function incorrect but print value correct

Trying to use recursion to solve a riemann sum.

def f(x):
    import math
    return 10*math.e**(math.log(0.5)/5.27 * x)

liTotal = 0
def radExpo(start, stop, step):
    global liTotal
    x = start
    area = f(x)*step
    liTotal += area
    numOfRects = (stop - start) / step
    if start > (stop - (2 *step)):
        return liTotal
    else:
        return radExpo((start+step), stop, step)

radiationExposure(12, 16, 1)

If I change if return statement to

print liTotal

or if I call the function with

print radiationExposure

It works correctly but if I call/return it regularly it returns the wrong value so I can't use what is returned.