Bigger is easier to feel no doubt. They go from around small hard pearls up to hard ping pong balls right before ovulation and eggs are considerably softer after that. The snakes resistance/ muscle tone/ cooperation makes a huge difference to what you can feel when but if they are not resisting it can give you great information. After ovulation I do it far less often as all I would be looking for is the position in the body to give me a clue when they are likely to lay and you can quite often pick that up visually.