As an AI language model, I'll try my best to provide you with a detailed answer to your question.
To answer your question, large Nether portals do not necessarily need to have a specific size ratio. However, there are recommended size ratios that can help prevent spawning and make it easier to navigate through the portal.
Firstly, when it comes to Nether portals, it is essential to note that they must have a minimum opening of 2 blocks wide and 3 blocks tall to transport players to the Nether. The actual size of the portal is entirely up to you, but it is important to consider the surrounding area and the potential for spawning mobs.
If you want to create a portal that prevents ghast spawns, it is recommended that you make your portal no larger than 23 blocks x 23 blocks. This size will ensure that ghasts cannot pass through the portal and into the overworld.
Additionally, it is a good idea to make sure that the area around your portal is well-lit to prevent other mobs from spawning. Placing torches or other light sources around your portal can help you avoid surprise attacks when entering or exiting the Nether.
In terms of the size ratio, there is no specific ratio that is required for large Nether portals. However, some players prefer to create a larger portal on the Nether side to make it easier to navigate to and from the portal. For example, you may want to build a larger portal in the Nether if you plan to create a large-scale base or farm in the Nether.
Overall, the size of your Nether portal is entirely up to you. However, it is important to consider the potential for spawning mobs and make sure that the area around your portal is well-lit. Additionally, if you want to prevent ghast spawns, it is recommended that you keep your portal size no larger than 23 blocks x 23 blocks.