diff --git a/fuzzers/030-iob18/top.py b/fuzzers/030-iob18/top.py
index e8f39805..6944e1ca 100644
--- a/fuzzers/030-iob18/top.py
+++ b/fuzzers/030-iob18/top.py
@@ -65,6 +65,15 @@ def run():
         "SSTL12":  DIFF_SSTL12,
     }
 
+    vref_map = {
+        "SSTL12":        .600,
+        "SSTL135":       .675,
+        "SSTL15":        .75,
+        "DIFF_SSTL12":   .600,
+        "DIFF_SSTL135":  .675,
+        "DIFF_SSTL15":   .75,
+    }
+
     only_diff_map = {
         "LVDS": ["LVDS"],
     }
@@ -99,13 +108,7 @@ def run():
     for iobank in iobanks:
         iostandard = random.choice(iostandards)
         if iostandard in SSTL:
-            params['INTERNAL_VREF'][iobank] = random.choice(
-                (
-                    .600,
-                    .675,
-                    .75,
-                    .90,
-                ))
+            params['INTERNAL_VREF'][iobank] = vref_map[iostandard]
 
         iostandard_map[iobank] = iostandard
 
diff --git a/fuzzers/030-iob18/write_io_banks.tcl b/fuzzers/030-iob18/write_io_banks.tcl
index eac330da..c433e5e8 100644
--- a/fuzzers/030-iob18/write_io_banks.tcl
+++ b/fuzzers/030-iob18/write_io_banks.tcl
@@ -11,7 +11,11 @@ open_io_design -name io_1
 set fp [open "iobanks.txt" "w"]
 foreach iobank [get_iobanks] {
     foreach site [get_sites -of $iobank] {
-        puts $fp "$site,$iobank"
+        # we only care about the high performance banks here
+        # and those are numbered 32, 33, 34...
+        if {[string match "3*" $iobank]} {
+            puts $fp "$site,$iobank"
+        }
     }
 }
 close $fp