Drawing Scaled grid system using openCV and python

Question

What I want to do is draw a grid on an image that has smaller squares at the top and larger ones near the bottom. I am lost on how to do this though. I figured out how to draw a grid on the image using open cv but don't know how to fine turn it to get the results I want.

What I will be using this for is to find where a bounding box point is for a detected object. I will need a smaller bounding box at the top and a larger one closer to the bottom of the image.

This is what I want to do:

But I cannot figure out how to get the curves in the code. This is what I have so far:

And this the is code that I am using.

'''
#This method draws simple grid overthe image based on the passed step
#The pxstep controls the size of the grid
'''
def drawBasicGrid(image, pxstep, midX, midY):
    x = pxstep
    y = pxstep
    #Draw all x lines
    while x < img.shape[1]:
        cv2.line(img, (x, 0), (x, img.shape[0]), color=(255, 0, 255), thickness=1)
        x += pxstep
    
    while y < img.shape[0]:
        cv2.line(img, (0, y), (img.shape[1], y), color=(255, 0, 255),thickness=1)
        y += pxstep
    

This draws the basic grid. and this creates thebounding boxes that I use for detection of the bounding points of a detected object.

def makeBoundingBox(h,w, step):
    #BBox is 100*100 square or step which is defied
    y = 0
    bbox = []
    while y < h:
        #print("Y value", y)
        x=0
        while x < w:
            #print("X Value", x)
            bbox.append([(x,y), (x+step, y+step)])
            x += step
        y += step
    
    return bbox

And this is how I am using it.

#Prepare Images
img = cv2.imread(image)
#img = imutils.resize(img, width=300)
#gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
(H,W) = img.shape[:2]
#Create bounding boxes for the image
'''
#Creates the boxes for people detection 
#It will look for which bounding boxes the person is in and then 
#Draw a box around their feet
'''
#People Detection
blob = cv2.dnn.blobFromImage(cv2.resize(img, (300, 300)),0.007843,(300, 300), 127.5)
net.setInput(blob)
detections = net.forward()
'''
#Get the center point of the image
'''
midY = H//2
midX = W//2
print("Middle Y pixel", midY)
#Draw center line
cv2.line(img, (0, midY), (W, midY), color=green, thickness=2)
cv2.line(img, (midX, 0), (midX, H), color=green, thickness=2)

#Visual grid drawn
drawBasicGrid(img, step, midX,midY)
bbox = makeBoundingBox(H, W, step) #Used for finding where the endx and startx BBOX  points are

Any help on this will be appreciated.