1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

t=int(input())
for i in range(t):
    n=int(input())
    a=[int(i) for i in input().split()]
    val=[]
    for i in range(n):
        if i==0:
            if a[i]>a[i+1]:
                val.append(i)
        elif i==n-1:
            if a[i]>a[i-1]:
                val.append(i)
        else:
            if a[i]>a[i+1] or a[i]>a[i-1]:
                val.append(i)
    if val==[]:
        print(-1)
        continue
    ind=0
    for i in range(len(val)):
        if a[val[i]]>a[val[ind]]:
            ind=i
    print(val[ind]+1)
            
    
    