How can I expand this Gabor patch to the size of the bounding box?

Question

I am trying to create a 2D image known as a variable size Gabor patch . Gabor's patch is best viewed as a convolution of a two-dimensional sine and 2D Gaussian.

The following is the function used to generate the code. The code has been ported from this tutorial for Matlab (suppose import numpy as np):

def gabor_patch(size, lambda_, theta, sigma, phase, trim=.005):
    """Create a Gabor Patch

    size : int
        Image size (n x n)

    lambda_ : int
        Spatial frequency (px per cycle)

    theta : int or float
        Grating orientation in degrees

    sigma : int or float
        gaussian standard deviation (in pixels)

    phase : float
        0 to 1 inclusive
    """
    # make linear ramp
    X0 = (np.linspace(1, size, size) / size) - .5

    # Set wavelength and phase
    freq = size / float(lambda_)
    phaseRad = phase * 2 * np.pi

    # Make 2D grating
    Xm, Ym = np.meshgrid(X0, X0)

    # Change orientation by adding Xm and Ym together in different proportions
    thetaRad = (theta / 360.) * 2 * np.pi
    Xt = Xm * np.cos(thetaRad)
    Yt = Ym * np.sin(thetaRad)
    grating = np.sin(((Xt + Yt) * freq * 2 * np.pi) + phaseRad)

    # 2D Gaussian distribution
    gauss = np.exp(-((Xm ** 2) + (Ym ** 2)) / (2 * (sigma / float(size)) ** 2))

    # Trim
    gauss[gauss < trim] = 0

    return grating * gauss

I would like the size of the Gabor patch to increase in proportion to the parameter size. In other words, I would like the size of the bounding box to determine the diameter of the patch. The problem is that this function does not behave this way. Instead, the bounding box grows in size, while the patch retains the same dimensions.

Example 1: size = 100

2: = 500

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