Entity Framework 6.0 NVarchar vs Varchar

Question

I have a site running in Azure that is causing me headaches. I see a select query as being an expensive query in Azure that is coming from EF.

The query is a select against a varchar column in the database, but from EF, it is turning it into nvarchar(4000), causing the query to time out.

Here is how I'm calling the query in the code:

var myObject = db.MyTable.FirstOrDefault(cm => cm.MyField == entryModel.MyField.Trim());

I have searched through many resources explaining how EF uses nvarchar instead of varchar, so I've tried adding this annotation to the field in my model class:

[Column(TypeName = "varchar(50)")]

When that didn't work, I tried adding this to the OnModelCreating method:

modelBuilder.Entity<MyTable>().Property(x => x.MyField).IsUnicode(false);

I've also tried this to force all strings to varchar:

modelBuilder.Properies<string>().Configure(x => x.HasColumnType("varchar(1000)"));

The query is still causing performance issues that, according to the activity monitor in the database, the query is still showing as this:

(@p__linq__0 nvarchar(4000))SELECT TOP (1) 

blah blah fields

FROM [dbo].[MyTable] AS [Extent1]

WHERE ([Extent1].[MyField] = (LTRIM(RTRIM(@p__linq__0)))) OR (([Extent1].[MyField] IS NULL) AND (LTRIM(RTRIM(@p__linq__0)) IS NULL))

Any ideas as to what is causing this? I'm at a point right now that I'm about to just write a stored procedure to call instead of using this EF query.

EDIT Thanks to @Robert Harvey and @StriplingWarrior for their help. Removing the inline trim allowed EF to recognize the varchar change as well as removing the TRIM from the actual SQL calls.

var myField = entryModel.MyField.Trim();
var myObject = db.MyTable.FirstOrDefault(cm => cm.MyField == myField);                                    

Thanks!

Aaron