I can't quote you chapter and verse on where to find it, but it is outdated. As long as the land to value ratio is typical of the area and supported with like type comps, it's ok. You probably are dealing with an underwriter who can't or won't think and use some judgement.
If the land to improvement ratio is way out of line, you may want to include some vacant sites like the subject to support your land value estimate, of course for an additional fee, if none are available, state so, so that they at least know you are aware of their concern and tried to provide additional relavent data.
If you get into a bind with them, you can always ask them that if their interpretation is true, how do waterfont properties ever get financed, are they all portfolio loans at and S&L, don't think so.
When the ratio is high, the lender may be concerned about the property having a use other that residential, address that fact.
And finally, they are guidelines, not rules that must be followed to the letter to make the property "fit". As long as you adress that fact that the guideline was not followed, you should be fine.